Radio technologies in cellular communications have grown rapidly and evolved since the launch of analog cellular systems in the 1980s, starting from the First Generation (1G) in 1980s, Second Generation (2G) in 1990s, Third Generation (3G) in 2000s, and Fourth Generation (4G) in 2010s (including Long Term Evolution (LTE) and variants of LTE). Fifth generation (5G) access networks, which can also be referred to as New Radio (NR) access networks, are currently being developed and expected to fulfill the demand for exponentially increasing data traffic, and to handle a very wide range of use cases and requirements, including among others mobile broadband (MBB) and machine type communications (e.g., involving Internet of Things (IOT) devices).
The upcoming 5G access network may utilize higher frequencies (e.g., >6 GHz) to aid in increasing capacity. Currently, much of the millimeter wave (mmWave) spectrum, the band of spectrum between 30 gigahertz (GHz) and 300 GHz is underutilized. The millimeter waves have shorter wavelengths that range from 10 millimeters to 1 millimeter, and these mmWave signals experience severe path loss, penetration loss, and fading. However, the shorter wavelength at mmWave frequencies also allows more antennas to be packed in the same physical dimension, which allows for large-scale spatial multiplexing and highly directional beamforming.
Performance can be improved if both the transmitter and the receiver are equipped with multiple antennas. Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The use of multiple input multiple output (MIMO) techniques, which was introduced in the third-generation partnership project (3GPP) and has been in use (including with LTE), is a multi-antenna technique that can improve the spectral efficiency of transmissions, thereby significantly boosting the overall data carrying capacity of wireless systems. MIMO techniques can improve mmWave communications, and has been widely recognized a potentially important component for access networks operating in higher frequencies. MIMO can be used for achieving diversity gain, spatial multiplexing gain and beamforming gain. For these reasons, MIMO systems, including massive MIMO systems using a large number of antennas, can be an important part of the 3rd and 4th generation wireless systems, and are planned for use in 5G systems.
The above-described background relating to wireless networks is merely intended to provide a contextual overview of some current issues, and is not intended to be exhaustive. Other contextual information may become further apparent upon review of the following detailed description.